The present invention generally relates to a recording and reproducing arrangement, and more particularly, to an optical information recording and reproducing apparatus such as a magneto-optical disc apparatus or the like for recording and reproducing signals with respect to a magneto-optical recording medium through utilization of magneto-optical effect.
Conventional optical information recording and reproducing apparatus of the type referred to above, are shown in FIG. 3, so that light emitted from a semi-conductor laser source 21 is incident upon a beam splitter 24 through a collimating lens 22 and a shaping prism 23, with nearly linearly polarized light perpendicular to an optical axis and parallel to the paper surface, being transmitted through the beam splitter 24. Light transmitted through the beam splitter 24 is incident upon an objective lens 26 through a mirror 25, and projected onto a disc 27 for the magneto-optical recording medium as a focused spot by said objective lens 26 so as to effect the recording function. During the reproducing function, light projected onto the disc 27 is subjected to the magneto-optical effect and proceeds through the objective lens 26 and the mirror 25 towards the beam splitter 24 in the form of reflected light so as to be reflected by said beam splitter 24. The reflected light is incident upon a polarizing beam splitter 29 through a 1/2 wavelength plate 28 and divided in two directions incident upon photo-detectors 30 and 31. The light rays thus incident upon the photo-detectors 30 and 31 and corresponding to the magnetizing direction of the disc 27 shown in FIG. 4(a). The light rays are converted into information signals S.sub.1 and S.sub.2 (electrical signals) as shown in FIGS. 4(b), and 4(c) so as to be applied to a differential amplifier 32. Thus, the signals are taken out as an information signal S.sub.D amplified two times, with the noise component of the same phase being cancelled as shown in FIG. 4(d), and the reproduction of the recorded information is to be effected by reproducing the information signal S.sub.D.
For detecting any recording error during the recording function in the conventional optical information recording and reproducing apparatus as described above, there have been known a practice for detection by effecting the reproducing function as referred to above, and another practice for detection which employs two light fluxes, one for recording and the other for reproduction following the light flux for the recording.
However, in the former practice as described above, the time for detecting the erroneous recording is approximately equal to that for recording. More specifically and for example, where the magneto-optical recording medium is in the form of a disc, the time required for the detection of the recording errors is equivalent to one rotation of the disc, thereby extremely obstructing recording at higher speeds in a shorter period of time.
In contrast, the latter practice requires a highly accurate optical system since the two light fluxes are adapted to be focused on the magneto-optical recording medium. Moreover, different driving circuits are respectively necessary for driving the two light sources, thus inviting such problems as complication in construction and consequent large size of the apparatus.